Method for manufacturing heat exchange vehicle

ABSTRACT

A method for manufacturing a novel heat exchanging vehicle comprising the steps of forming an inorganic surface layer over a cold rolled, aluminum or aluminum alloy sheet; treating the inorganic surface layer with a phosphoric compound solution; annealing the sheet; and forming the sheet into a predetermined shape. The resulting heat exchanging vehicle such as a fin has a good wettability and a high corrosion resistance to white rust based on the uniformity of the said surface layer.

BACKGROUND OF THE INVENTION

The present invention relates to a novel method for manufacturing a heatexchanging vehicle made of aluminum or an aluminum alloy, such as a heatexchanging fin, for use in an automobile or a home air conditioner, etc.

A heat exchanging fin made of aluminum or an aluminum alloy (hereinafterreferred to simply as "aluminum") is generally manufactured, forinstance, by forming a surface layer of organic or inorganic materialsor composite materials mentioned above having good wettability over analuminum sheet, pressing the aluminum sheet provided with such ahydrophilic surface layer to form a fin, and removing the lubricatingoil such as a pressing oil attached to the fin surface during thepressing operation with a neutral or weak alkaline detergent aqueoussolution, or by other means.

Recently, the fin pitch in heat exchanging units has been reduced forthe improvement of heat exchanging efficiency and the miniaturization ofheat exchangers. In an evaporator, such a reduced fin pitch causes thecondensation of atmospheric moisture on fins, increasing resistance toan air stream, generating noises and blowing condensed water into aroom. Further, it necessitates more energy for defrosting outdoors inwinter time. As a result, it is extremely important that the fin surfacehave good wettability and high resistance to oil stain.

In addition, the fins should have a good corrosion resistance to whiterust to prevent the formation of such a product which easily peels off.

To deal with these problems, the inventors have previously proposed amethod for manufacturing a heat exchanging vehicle by forming a surfaceoxide layer with a weight of about 0.2-1.0 g/m² over an aluminum sheetand forming it into a desired shape (Japanese Patent Laid-Open No.58-106396). This proposal, however, is not completes satisfactory.

It has been found that when a precoated sheet is formed into a fin bypressing, degreased with an organic solvent such as a trichloroethyleneto remove a lubricating oil which is attached during the pressingoperation from a fin surface, and then assembled into an evaporator, thefin surface does not always have good wettability and high resistance tooil stain, depending upon degreasing conditions such as degreasing bathtemperature and oil concentration in the degreasing bath, and theconditions of an inorganic surface layer such as an anodic oxidationlayer and a hydrated layer, etc.

A fin sheet is usually obtained by annealing a so-called H1n-tempersheet of a predetermined thickness manufactured by cold rolling to aso-called H2n- or O-temper sheet having the desired mechanicalproperties.

Therefore, oil components remain on the aluminum sheet surface withoutbeing evaporated during annealing. These components become scorched,adhere to the surface and make it rough even after the formation of anhydrated surface layer. As a result, good wettability and high corrosionresistance to white rust are not necessarily obtained.

OBJECT AND SUMMARY OF THE INVENTION

An object of the present invention is, therefore, to provide a methodfor manufacturing a novel heat exchanging vehicle having goodwettability and high corrosion resistance to white rust.

Another object of the present invention is to provide a method formanufacturing a heat exchanging vehicle which may be easily formed.

In view of the above objects, the inventors have carried out extensiveresearch. As a result, they have found that a heat exchanging vehiclehaving good wettability and high corrosion resistance to white rust canbe obtained by forming an inorganic surface layer over a cold-rolledaluminum sheet such as an H1n-temper sheet, wherein n is, for instance,2, 4, 6 or 8, by treating the inorganic surface layer with an aqueoussolution containing a phosphoric compound to spread the phosphoriccompound over surrface layer, annealing the aluminum sheet to convert itto an H2n- or O-temper sheet having the desired mechanical propertieswherein n is, for instance, 2, 4, 6 or 8, and then forming it into adesired shape. Such a heat exchanging vehicle has good and uniformwettability regardless of degreasing conditions and corrosion resistanceto white rust. This method is efficient, easy and provides a high yield.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inorganic surface layer formed over an H1n-temper sheet according tothe present invention may be an anodic oxidation surface layer or ahydrated surface layer such as a boehmite surface layer formed byimmersing in a boiling pure water, a boehmite surface layer treated witha basic aqueous solution at pH 9-12 adjusted with triethanolamine,ammonia water and sodium hydroxide, etc., a surface layer formed by thetreatment at a basic aqueous solution of pH 9-12 treated with oxidantssuch as XO⁻, XO₂ ⁻, XO₃ ⁻ (X being halogen), peroxyborate disclosed inJapanese Patent Laid-Open No. 59-211578, a silicate compound surfacelayer formed over the said anodic oxidation layer, the said hydratedlayer, a chromate layer, or a silicate compound surface layer alone.These inorganic surface layers having a good wettability are finelyporous, having a pore size of about 100-500 Å in the anodic oxidationsurface layers, about 500-2000 Å in the hydrated surface layers, andabout 3000-10000 Å in the silicate surface layers. Such a surface layermay have a weight of about 0.2-1.0 g/m², more preferably about 0.4-0.8g/m².

Among those inorganic surface layers, a hydrated surface layer or ahydrated surface layer covered with a extremely thin silicated layerafter hydration are particularly preferred because their surfaceconditions and porosity permit the phosphoric compound to adhereuniformly thereto.

The phosphoric compound on the inorganic surface layer may be easilyformed by treating the surface layer with an aqueous solution containingthe phosphoric compound and drying it. For instance, it may be easilyformed by dissolving the phosphoric compound in deionized water, tapwater or an industrial water at a concentration of 50 ppm or more, butmore preferably at a lower concentration of about 1-20 ppm, adjustingthe phosphoric compound aqueous solution to have pH of 2-12, preferably6-8, and subjecting the surface layer to immersion or showering with thephosphoric compound aqueous solution at temperature of 10°-100° C., forone second to 10 minutes, preferably 5-20 seconds. The pH adjustment ofthis solution may be conveniently achieved using phosphoric acid, citricacid, tartaric acid, acetic acid, sulfuric acid, sodium hydroxide,potassium hydroxide, calcium hydroxide, triethanolamine, ammonia waterand the like. The adjusting agent will be selected on the basis of thephosphoric compound employed. The phosphoric compound is defined on theinorganic surface layer at a preferred density of about 0.005-0.15 g/m²calculated on the basis of phosphorus.

The phosphoric compounds which may be used alone or in combination inthe present invention include inorganic phosphoric compounds such ashypophosphite, orthophosphite, metaphosphite, hypophosphate,orthophosphate, metaphosphate, monoperoxyphosphate, peroxydiphosphate,tripolyphosphate, tetrapolyphosphate, pyrophosphate, etc., inorganicphosphate esters such as myo-inositol diphosphate, myo-inositoltriphosphate, myo-inositol tetraphosphate, myo-inositol pentaphosphate,myo-inositol hexaphosphate, etc., water-soluble salts of the aboveinorganic phosphate esters in which hydrogen of the combined phosphatesis substituted with Na, K, Li, Mg, Ca, etc., phosphonic compounds suchas 1-hydroxypropane-1,1-diphosphonic acid;1-hydroxy-1-phenylmethane-1,1-diphosphonic acid;1-hydroxyethane-1,1-diphosphonic acid; 1-aminoethane-1,1-diphosphonicacid; dimethylaminobutane-1,1-diphosphonic acid; aminotrimethylenephosphonic acid; ethylenediaminetetramethylene phosphonic acid;phosphonic succinic acid; 1-phosphone-1-methylsuccinic acid; etc., andwater-soluble salts of these phosphonic compounds with sodium,potassium, ammonium, alkanolamine, etc.

In the treatment with a phosphoric compounds aqueous solution, nonionicsurfactants are preferably added in a small amount, e.g. about 0.1-2%.The inclusion of the nonionic surfactant together with the phosphoriccompound in the inorganic surface layer makes it easier to conduct thepress-forming operations which is carried out after annealing.

The nonionic surfactants which may be used alone or in combination inthe present invention may include polyoxyethylenealkylallyl ether type(polyoxyethylenenonyl-phenyl ether, polyoxyethyleneoctylphenyl ether),alkyl ether type (polyoxyethylenelauryl ether), alkyl ester type(polyoxyethylene oleate), alkylamine type (polyoxyethylenelaurylamine),ester type of sorbitan derivatives (sorbitan laurate, sorbitanpalmitate), sorbitan derivatives compound type(polyoxyethylenesorbitanlaurate polyoxyethylenesorbitanstearate), etc.

The cold rolled H1n-temper sheet formed with the inorganic surface layerincluding the phosphoric compound (and preferably containing thenonionic surfactant) is annealed at 200°-450° C. for 1 second-20 hoursin a batch process or a continuous process, preferably at 200°-360° C.for 3-20 hours in a batch process to provide an H2n- or O-temper sheethaving the desired properties.

In this process, it is to be noted that the aluminum sheet is subjectedto a surface treatment just after cold rolling. Therefore, the problemencountered in the conventional method in which oil components stickingon the sheet surface are scorched can be avoided. The appearance of theformed sheet is uniform. Thus, the H2n- or O-temper sheet with a surfacehaving good wettability and a high corrosion resistance to white rust isobtained.

The H2n- or O-temper sheet formed with such a surface layer having goodwettability and high corrosion resistance to white rust is thensubjected to forming such as drawless-pressing or draw-pressing.Lubricating oil such as pressing oil remaining on the sheet surfaceafter the press forming may be removed by a neutral or weak-alkalineaqueous solution or an organic solvent such as trichloroethylene toprovide the desired fins.

Since the heat exchanging vehicle thus obtained has an inorganic surfacelayer including the phosphoric compound, fine pores of the inorganicsurface layer have been modified, so that the surface layer tends toprevent the adsorption of pressing oil. Thus, the inorganic surfacelayer retains its good original wettability. Further, it has an improvedcorrosion resistance to white rust even after annealing. This surfacelayer makes it unnecessary to carry out the troublesome process forremoving the pressing oil. Further, a high productivity is ensured.

The present invention will be explained in further detail by thefollowing Examples.

EXAMPLE 1

An aluminum sheet of H18-temper (JIS1200) having a 800-mm width, a8000-m length and a 0.115-mm thickness was degreased with weak alkalineaqueous solution, and immersed in an aqueous solution of sodiumhypochlorite (NaOCl concentration: 2000 ppm, pH 10.5) at about 85° C. toform a hydrated surface layer of about 0.6 g/m² thickness having a poresize of about 500-1000 Å.

Next, it was immersed in a 1.5%-water glass aqueous solution (pH 11.4)at about 60° C., washed with water shower, and then formed with anextremely thin silicate surface layer having a thickness of about 0.025g/m² based on silicon.

An aqueous solution of 2% sodium tripolyphosphate and0.5%-polyoxyethylene nonylphenylether (HLB value 14) was applied overthe sheet at 25°-30° C., and it was dried with hot air at 150° C. for 10seconds. Thus, the inorganic phosphate at a weight of about 0.015 g/m²based on phosphorus and 0.008 g/m² of the nonionic surfactant wereincluded over the hydrated surface layer treated with water glassaqueous solution.

The sheet was annealed in a furnace at 260° C. to convert it to anH26-temper sheet.

The H26-temper sheet was subjected to drawless-pressing to form fins,and then immersed in trichloroethylene heated at about 80° C. for oneminute to remove any remaining oil. It was then assembled into a heatexchanger.

EXAMPLE 2

Instead of treatment with sodium tripolyphosphate and polyoxy ethylenenonylphenylether as in Example 1, an immersion treatment was carried outwith an aqueous solution of 5% 1-hydroxy ethane-1,1-diphosphonic acid,5%-5Na salt of aminotrimethylene phosphonic acid and 1% polyoxyethyleneoleate at 50° C. A similar drying operation with hot air was performedto include the phosphonic compound at a weight of 0.08 g/m² based onphosphorus and 0.02 g/m² of the nonionic surfactant over the hydratedsurface layer treated with water glass aqueous solution.

The same annealing was carried out for the sheet as in Example 1,converting it to an H26-temper sheet, which was then subjected to adrawless-pressing to provide fins. The fins were degreased withtrichloroethylene (immersion at 50° C., 30° C. and 70° C. each for oneminute). They were then assembled into a heat exchanger.

EXAMPLE 3

The same aluminum sheet as in Example 1 was degreased with a weakalkaline aqueous solution, washed with water and then dried. It was thenimmersed in an aqueous solution of 0.5%-triethanolamine at 90° C. for 60seconds to perform a boehmite treatment to form a hydrated inorganicsurface layer having a weight of 0.4 g/m², a pore size of about 800-2000Å and good wettability. It was then treated with an aqueous solution of2% myo-inositol hexaphosphoric acid ester and 0.5% polyoxyethylenesorbitan laurate (HLB value 15.4) at 25°-30° C. It was dried with hotair at 150° C. for 10 seconds to form a surface layer of the phosphateester with myo-inositol at a weight of 0.03 g/m² based on phosphorus and0.015 g/m² of the nonionic surfactant over the hydrated surface layer.

It was then annealed in a non-oxidative furnace at 300° C. for 8 hoursto convert it to a O-temper sheet.

Draw-pressing was then performed to form fins, which were degreased asin Example 2. The fins were finally assembled into a heat exchanger.

EXAMPLE 4

The same aluminum sheet as in Example 1 was subjected to anodicoxidation in an aqueous solution of 15% sulfuric acid to form a porousanodic oxidation surface layer having a weight of 0.6 g/m² and pore sizeof 100-150 Å. It was treated with a solution containing the samephosphoric compound and the same nonionic surfactant as in Example 1, sothat the anodic-oxidation surface layer included the inorganic phosphateat a weight of 0.015 g/m² based on phosphorus and 0.008 g/m² of thenonionic surfactant. The same annealing was then conducted and the samedrawless-pressing was carried out to form fins. They were furtherdegreased as in Example 2 and assembled into a heat exchanger.

EXAMPLE 5

The same aluminum sheet as in Example 1 was immersed in an aqueoussolution of sodium silicate (SiO₂ /Na₂ O=5, SiO₂ concentration=55 g/l)at 60° C. for one minute, and dried at 200° C. for 60 seconds to form asilicate surface layer having a weight of 0.8 g/m² and a pore size ofabout 3000-5000 Å. It was then treated with a solution containing thesame phosphoric compound and the same nonionic surfactant as in Example1 to deposit an inorganic phosphate layer weighing about 0.015 g/m²based on phosphorus and 0.008 g/m² of the nonionic surfactant. The sameannealing was conducted. Thereafter, the sheet was subjected todrawless-pressing to form fins, which were degreased and assembled intoa heat exchanger.

Comparative Examples 1-5

The same treatments as in Examples 1-5 were performed except foromitting the treatment with the aqueous solution containing phosphoriccompounds and nonionic surfactants.

Comparative Example 6

The same treatments as in Example 1 were performed except for omittingthe treatment of forming the inorganic surface layer.

Comparative Example 7

The same aluminum sheet as in Example 1 was annealed to provide anH26-temper sheet, which was then subjected to the same surface treatmentas in Example 1 and drawless-pressing to form fins. It was degreased andthen assembled into a heat exchanger.

Properties

With respect to the aluminum heat exchanger fins obtained as mentionedabove, uniformity of surface layers, wettability (contact angle forwater drop) after assembly into heat exchangers and degreasing,formability and corrosion resistance to white rust after cycle test ofdrying and wetting for 5 days (7 hour a day in a wet condensed conditionby cooling the fins) in an atmosphere of 40° C., 85% RH wereinvestigated. The results are shown in the following table.

                  TABLE                                                           ______________________________________                                                                           Corrosion                                  Uniformity                         Resistance                                 of Surface    Contact              to White                                   Layer         Angle (°)                                                                       Formability Rust                                       ______________________________________                                        Example 1                                                                             Uniform   10       No crack and                                                                            No White                                                            No punch-out                                                                            Rust                                     Example 2                                                                             "         "        No crack and                                                                            No White                                                            No punch-out                                                                            Rust                                     Example 3                                                                             "         "        No crack and                                                                            No White                                                            No punch-out                                                                            Rust                                     Example 4                                                                             "         "        No crack and                                                                            No White                                                            No punch-out                                                                            Rust                                     Example 5                                                                             "         "        No crack and                                                                            No White                                                            No punch-out                                                                            Rust                                     Compara-                                                                              "         40       A Few Cracks                                                                            Entirely                                 tive                                 Covered                                  Example 1                            with White                                                                    Rust                                     Compara-                                                                              "         45       "         Entirely                                 tive                                 Covered                                  Example 2                            with White                                                                    Rust                                     Compara-                                                                              "         60       "         Entirely                                 tive                                 Covered                                  Example 3                            with White                                                                    Rust                                     Compara-                                                                              "         50       "         Entirely                                 tive                                 Covered                                  Example 4                            with White                                                                    Rust                                     Compara-                                                                              "         40       "         Entirely                                 tive                                 Covered                                  Example 5                            with White                                                                    Rust                                     Compara-                                                                              --        55       "         Little                                   tive                                 White Rust                               Example 6                                                                     Compara-                                                                              Uneven    40       No crack and                                                                            Little                                   tive                       No punch-out                                                                            White Rust                               Example 7                                                                     ______________________________________                                    

As is apparent from the above, the fins according to the presentinvention are superior to those of the comparative examples with respectto surface layer uniformity, water contact angle (wettability),formability and corrosion resistance to white rust. Thus, fins having agood heat exchanging efficicency and durability are obtained at a highyield.

What is claimed is:
 1. A method for manufacturing a heat exchanging vehicle, comprising the steps of:(a) forming an inorganic surface layer over a cold-rolled sheet of aluminum or an aluminum alloy; (b) treating said inorganic surface layer with an aqueous solution containing a phosphoric compound to deposit said phosphoric compound on said inorganic surface layer; (c) annealing said sheet; and (d) forming said sheet into a heat exchanging vehicle.
 2. The method according to claim 1, wherein said cold-rolled sheet of aluminum or an aluminum alloy is an H1n-temper sheet wherein n represents 2, 4, 6 or
 8. 3. The method according to claim 1, wherein said inorganic surface layer has a weight of about 0.2 to 1.0 g/m².
 4. The method according to claim 1, wherein said inorganic surface layer is covered with silicate compounds.
 5. The method according to claim 1, wherein said inorganic surface layer is a hydrated surface layer.
 6. The method according to claim 5, wherein said hydrated inorganic surface layer is covered with an extremely thin silicate layer.
 7. The method according to claim 1, wherein said inorganic surface layer is an anodic-oxidation surface layer.
 8. The method according to claim 7, wherein said anodic-oxidation inorganic surface layer having a good wettability is covered with an extremely thin silicate layer.
 9. The method according to claim 1, wherein said phosphoric compound is selected from the group consisting of inorganic phosphoric, compounds inorganic phosphate esters, water-soluble salts of said inorganic phosphate esters, phosphonic acid compounds, water-soluble salts of said phosphonic acid compounds, and mixture thereof.
 10. The method according to claim 1 wherein the weight of said inorganic surface layer is about 0.005 to 0.15 g/m² based on phosphorus.
 11. The method according to claim 1, wherein said phosphoric compound aqueous solution contains at least 50 ppm of said phosphoric compound.
 12. The method according to claim 1, wherein said solution containing said phosphoric compound additionally contains a nonionic surfactant.
 13. The method according to claim 12, wherein the concentration of said nonionic surfactant is about 0.1 to 2%.
 14. The method according to claim 1, wherein annealing is conducted at about 200° to 450° C. from 1 second to 20 hours.
 15. The method according to claim 1, wherein said organic surface layer has a weight of 0.4 to 0.8 g/m².
 16. The method according to claim 1, wherein said phosphoric compound solution contains 1 to 20 ppm of said phosphoric compound.
 17. The method according to claim 1, wherein annealing is conducted at 200° to 260° C. for 3 to 20 hours.
 18. The method according to claim 1, wherein said aluminum or aluminum alloy sheet is an H2n- or O-temper sheet wherein n is 2, 4, 6 or
 8. 19. A heat exchanging vehicle formed by the steps comprising:(a) forming an inorganic surface layer over a cold-rolled sheet of aluminum or an aluminum alloy; (b) treating said inorganic surface layer with an aqueous solution containing a phosphoric compound to deposit said phosphoric compound on said inorganic surface layer; (c) annealing said sheet; and (d) forming said sheet into a heat exchanging vehicle.
 20. The vehicle according to claim 19, wherein said cold-rolled sheet of an aluminum or an aluminum alloy is an H1n-temper sheet wherein n represents 2, 4, 6 or
 8. 21. The vehicle according to claim 20, wherein said solution containing said phosphoric compound additionally contains a nonionic surfactant.
 22. The vehicle according to claim 21, wherein said nonionic surfactant is at a concentration of about 0.1 to 2%.
 23. The vehicle according to claim 19, wherein said inorganic surface layer has a weight of about 0.2 to 1.0 g/m².
 24. The vehicle according to claim 19, wherein said inorganic surface layer is covered with silicate compounds.
 25. The vehicle according to claim 19, wherein said inorganic surface layer is a hydrated surface layer.
 26. The vehicle according to claim 25, wherein said hydrated inorganic surface layer is covered with an extremely thin silicate layer.
 27. The vehicle according to claim 15, wherein said inorganic surface layer is an anodic-oxidation surface layer.
 28. The vehicle according to claim 27, wherein said anodic-oxidation inorganic surface layer is covered with an extremely thin silicate layer.
 29. The vehicle according to claim 17, wherein said phosphoric compound is selected from the group consisting of inorganic phosphoric compounds, inorganic phosphate esters, water-soluble salts of said inorgranic phosphate esters, phosphonic acid compounds and water-soluble salts of said phosphonic acid compounds and mixtures thereof.
 30. The vehicle according to claim 19, wherein the weight of said inorganic surface layer is about 0.005 to 0.15 g/m² based on phosphorus.
 31. The vehicle according to claim 19, wherein said phosphoric compound aqueous solution contains at least 50 ppm of said phosphoric compound.
 32. The vehicle according to claim 19, wherein said annealing is carried out at about 200° to 450° C. for 1 second to 20 hours.
 33. The vehicle according to claim 19, wherein said aluminum or aluminum alloy sheet after annealing is an H2n- or O-temper sheet wherein n is 2, 4, 6 or
 8. 34. The vehicle according to claim 19, wherein said organic surface layer has a weight of 0.4 to 0.8 g/m².
 35. The vehicle according to claim 19, wherein said phosphoric compound aqueous solution contains 1 to 20 ppm of said phosphoric compound.
 36. The vehicle according to claim 19, wherein said annealing is conducted at 200° to 360° C. for 3 to 20 hours. 